scott.marlowe wrote:
>
>OK, but here's the real test. As the postgres user, run 'pgbench -i',
>then after that runs, run 'pgbench -c 50 -t 1000000'. While it's running
>and settled (pg aux|grep postgres|wc -l should show a number of ~54 or
>so.) pull the plug. Wait for the hard drives to spin down, then plug it
>back in and power it one. With SCSI you will still have a coherent
>database.
>
>
Agreed in principle - pgbench is the most interesting test... for this
mailing list anyway :-).
However s = 1 makes a tiny database that fits into the file buffer cache
on most machines, which is not a very realistic situation.
e.g. the Dell gets tps = 250 for s = 1 c = 5 t = 1000. This number
looks great but its not too much to do with IO....
I am happier about s = 10 - 50 for machines with 512+ Mb of RAM.
From memory the Dell gets tps = 36 for s = 10 c = 5 t = 100000. This
result seems more believable!
>If you want a coherent database on IDE drives under postgresql you will
>need to issue this command: 'hdparm -W0 /dev/hdx' where x is the letter of
>the drives under the RAID array to turn off write caching. This will slow
>them to a crawl on writes.
>
>
I should have said that I was using Freebsd 4.8 with write caching off.
The question of whether the disk *actually* turned it off is the
significant issue, so yes, "use with care" should preface any comments
about IDE usage!
best wishes
Mark